Improve the architecture by configuring the playlist handle directly
in register_playlist() instead of deferring it to run().
Changes:
- Remove playlist_handle_pending field (no longer needed)
- register_playlist() now calls logic_mut() to configure immediately
- run() becomes a simple delegation with no configuration logic
- Follows proper pattern: configuration before run(), not during run()
This is cleaner than the previous approach which used a pending field
and transferred it during run(). The new approach:
1. User calls register_playlist() → directly configures logic
2. User calls run() → simple delegation to inner.run()
Architecture now properly separates configuration from execution.
- Add Node::logic_mut() method to allow post-construction configuration
of node logic before run() is called
- Fix FlacCacheSink to properly transfer playlist_handle_pending to
the inner logic using logic_mut()
- Resolves FIXME at flac_cache_sink.rs:656 about missing logic_mut()
This enables the playlist registration mechanism to work correctly:
1. User calls register_playlist() on FlacCacheSink
2. Handle is stored in playlist_handle_pending
3. During run(), handle is transferred to FlacCacheSinkLogic
4. Tracks are automatically added to playlist after caching
